The invention relates to a combined transformer for an LLC resonant converter and to an LLC resonant converter having such a transformer, where LLC refers to a configuration with two inductors (LL) and a capacitor (C).
In on-board charging devices, so-called galvanically isolated DC/DC converters are often used for reasons of efficiency. The galvanic isolation is required here for reasons of safety. The galvanically isolated energy transmission can be achieved by using a transformer. A conventional topology for such a resonant galvanically isolated DC/DC converter is the so-called LLC topology, which is distinguished by a resonant network consisting of a series resonant inductor, a parallel resonant inductor and a resonant capacitor. The parallel resonant inductor is usually realized by the main inductance of the transformer and therefore does not constitute an additional component part. As a result, it is possible for switching transistors to be able to be used for switching over the entire load range under zero voltage (so-called zero-voltage switching), as a result of which energy-efficient operation with high efficiencies can be achieved. Resonant converters of this kind also have a high power density.
Beyond these achievements, a further reduction of the necessary installation space is desirable.
The present invention is therefore based on the object of reducing the installation space of an LLC resonant converter. Furthermore, the invention is intended to be used to reduce the costs of producing the LLC resonant converter and the weight thereof as well as to improve the simplicity in terms of the design thereof.
According to the invention, the above object is achieved by the features of the independent claim. Advantageous embodiments are described in the dependent claims.
The combined transformer according to the invention for an LLC resonant converter comprises a primary transformer winding, which is configured to generate during operation a first magnetic flux, for example in the transformer core, which first magnetic flux forms a first magnetic circuit, and a resonant inductor having a winding, which resonant inductor is configured to generate during operation a second magnetic flux, which forms a second magnetic circuit. The primary transformer winding and the winding of the resonant inductor are arranged with respect to one another in such a way that at least one first part of the first magnetic circuit and at least one second part of the second magnetic circuit run on a magnetic path common to the first part and to the second part.
A transformer comprises a primary and a secondary winding on a common core. The combined transformer according to the invention comprises the winding of the resonant inductor, which can be integrated in a single component together with the transformer core and the transformer windings. The primary transformer winding and the winding of the resonant inductor can be wound onto a common core, for example the transformer core in the form of a three-limbed core, or on cores adjoining one another that are different from one another. The primary transformer winding is coupled to the winding of the resonant inductor. The primary-side transformer winding and the winding of the resonant inductor form in each case a magnetic circuit, wherein the magnetic circuits of the primary-side transformer winding and the winding of the resonant inductor run at least partly on a magnetic path common to the two circuits or the primary-side winding and the resonant inductor have at least one section of their respective circuit in common.
The transformer winding generates a magnetic circuit, the so-called transformer circuit. The winding of the resonant inductor generates a further magnetic circuit, the so-called resonant circuit. There is now provision according to the invention for the resonant circuit and the transformer circuit to share at least a part of their magnetic circuits. This sharing can be seen in spatial terms, that is to say it takes place at the same location. The common part of the magnetic circuits, which are generated by the transformer winding and the winding of the resonant inductor, also referred to as common section, is the common magnetic path. Together with the secondary winding of the transformer, according to the invention there is thus a transformer combined or coupled with a resonant inductor present as an integrated component.
In the following text, the transformer is always understood as the physical transformer, wherein the addition of “ideal” specifically refers to the ideal transformer.
According to the invention, a combined transformer, and, in one embodiment, a combined LLC transformer, are proposed. The design of the combined transformer is distinguished by a combined arrangement of the magnetic resonant component parts and the transformer. The inventive integration of the magnetic resonant component parts can achieve the savings to be achieved according to the object of the present invention in the area of number of component parts, installation space, costs and weight. The combined LLC transformer can also be realized without extra component parts. For example, no further components are necessary for the design of the combined transformer in comparison with an LLC resonant converter with transformer and resonant inductor separate therefrom.
In one embodiment of the combined transformer according to the invention, the primary transformer winding and the winding of the resonant inductor are arranged with respect to one another in such a way that the first magnetic flux of the first magnetic circuit and the second magnetic flux of the second magnetic circuit are at least partly destructively superposed on the magnetic path common to the first part and to the second part. The resonant component parts in the form of the resonant inductor having a resonant inductance value and the transformer having a magnetizing inductance value are thus arranged or interconnected in such a way that the magnetic fluxes of the magnetic circuits are completely or partly destructively superposed on the common magnetic path.
The destructive superposition of the magnetic fluxes, that is to say the at least partial subtraction thereof, causes the material or medium that penetrates the magnetic flux to have a lower overall flux density in this part of the common magnetic path than without the destructive superposition. In this way, the required magnetic cross section at the location of the common path can be reduced in comparison with a non-destructive superposition given identical magnetic fluxes. The flux resulting from the two magnetic fluxes is smaller than the respective magnetic fluxes (individual fluxes) separately. More precisely, the destructive superposition causes the magnitude of the resulting flux to be smaller than the magnitude of the larger flux of the two magnetic fluxes guided on the common path.
In a further embodiment of the combined transformer according to the invention, the destructive superposition is caused by an arrangement, winding direction and/or interconnection of the primary transformer winding and the resonant inductor.
The arrangement denotes the position or positioning of the resonant inductor and the primary transformer winding with respect to one another. If the resonant inductor and the primary transformer winding are placed on a core, they can be located on respectively one of a plurality of possible limbs of a core. The core type is in turn selected from a plurality of possible types of core. The winding direction of the resonant inductor and the primary transformer winding determines the respective direction of the magnetic flux. Depending on the arrangement and interconnection, the resonant inductor and the primary transformer winding are wound in the opposite direction or in the same direction. The interconnection of the resonant inductor and the primary transformer winding influences the temporal sequence and direction in which current flows through the resonant inductor and the primary transformer winding. The temporal sequence and direction in which current flows through the resonant inductor and the primary transformer winding determines (in addition to the arrangement and the winding direction) when and in which direction the magnetic fluxes are generated.
One possible interconnection can be effected by a simple, where appropriate direct, electrical connection without intermediate elements respectively of a terminal of the resonant inductor and the primary transformer winding with one another. In this series circuit of the resonant inductor and the primary transformer winding, the same current flows through the resonant inductor and the primary transformer winding. This ensures that in each case a magnetic flux is generated at the same time in the resonant inductor and the primary transformer winding so that said respective magnetic fluxes can be superposed in the same magnetic path (at any time).
The combination of the arrangement of the resonant inductor and the primary transformer winding, winding direction and/or interconnection takes place according to the invention in such a way that the magnetic fluxes of the resonant inductor and the primary transformer winding in the common magnetic path partly or completely destructively add up.
In one particular embodiment of the combined transformer according to the invention, the first magnetic circuit and the second magnetic circuit are guided along a core.
In a further embodiment of the combined transformer according to the invention, the first magnetic circuit and the second magnetic circuit are guided at least partly along respective core segments of the core.
The core serves for the targeted spatial guidance of the magnetic flux in the magnetic circuit and usually consists of materials with a high magnetic conductivity, such as ferrite or iron, for example.
The core can consist of a plurality of core segments. In this case, there are at least two parts of the core, through each of which one of the magnetic fluxes flows independently of one another. A core can also have more than two core segments. In one embodiment, the two magnetic fluxes can be guided together on a part of the core, for example in a common limb.
The halves of the core can each be arranged in a circular manner in a circuit end, such as, for example, in the case of an EI core form or else can be embodied as single limbs with possibly open ends.
In a further embodiment of the combined transformer according to the invention, a magnetically active cross section of the core at a location of the magnetic path common to the first part and to the second part is reduced with respect to another location outside of the magnetic path common to the first part and to the second part.
The destructive superposition causes an overall flux that is lower in comparison with destructive superposition not being present. In other words: the magnetic flux is lower at this location due to the destructive superposition than at a location outside of the common path. In order to retain the same magnetic flux density, in the case of a lower magnetic flux, the magnetically active cross section of the material/medium at the location of the common path can be selected to be smaller. In this way, a thinner material/medium and/or a material/medium with a lower cross section at this location is possible than at a location without the destructive superposition. As a result, the volume and the installation space of the combined transformer according to the invention can be reduced.
The cross section of the material/medium orthogonal to the flux direction of the magnetic flux is defined as the magnetically active cross section. Since this magnetic flux usually runs along or approximately parallel to the longitudinal extent of a material/medium of the core, the magnetically active cross section usually corresponds to the cross section of the material/medium.
In order to reduce the required magnetic cross section, the resonant inductor and the primary transformer winding are furthermore interconnected and wound in such a way that the magnetic flux is destructively added on the common path.
The cross section of the material/medium of the core can be reduced in comparison with a cross section of the material/medium of the core at locations that are not situated on the common path of the magnetic circuits. The thickness or the cross section of the core can thus be smaller in the destructively superposed part of the common path than in the regions of the core, for example the core halves, on which the magnetic fluxes are not guided together. In another approach, the magnetically active cross section of the core can be reduced in comparison with the cross section that would be necessary if the magnetic fluxes were not destructively added. If they were added, for example, in a positive manner, the cross section would have to be even larger than at locations through which only one of the two magnetic fluxes flows.
In one particular embodiment of the combined transformer according to the invention, the primary transformer winding and the winding of the resonant inductor are wound onto different limbs of the core. Open limbs make it possible to easily wind the resonant inductor and the primary transformer winding around the core. In the case of closed circuits or cores, the wire for each winding has to be threaded through in a complex manner. If necessary for a specified application, the resonant inductor and the primary transformer winding can each be wound onto rings or half-shells.
In one embodiment according to the invention of the combined transformer, the core is embodied as a PQ or E core. For these cores, there may be matching winding bodies, which permit the prefabrication, the separate assembly of the winding on the core and the connection of the winding, for example to a printed circuit board.
In a further embodiment of the combined transformer according to the invention, the primary transformer winding and the winding of the resonant inductor are wound in one piece. In this way, the winding of the resonant inductor and the primary transformer winding can be wound using a single wire. This winding process is ideally carried out in one working step, which simplifies production. In this case, first of all, a first winding can be wound around a limb, the wire can then be guided to a second limb and the second winding can be wound there using the same apparatus.
In one particular embodiment of the combined transformer according to the invention, there is provision for the combined transformer to be used as an LLC transformer when the resonant inductor is electrically connected to a capacitor. The interconnection with the capacitor can achieve a circuit having a connected resonant circuit.
The invention furthermore comprises an LLC resonant converter having a combined transformer, which comprises a primary transformer winding, which is configured to generate during operation a first magnetic flux, which forms a first magnetic circuit, and has a resonant inductor having a winding, which resonant inductor is configured to generate during operation a second magnetic flux, which forms a second magnetic circuit, wherein the primary transformer winding and the winding of the resonant inductor are arranged with respect to one another in such a way that at least one first part of the first magnetic circuit and at least one second part of the second magnetic circuit run on a magnetic path common to the first part and to the second part.
A previous multi-component-part arrangement of the resonant inductor, the primary transformer winding and the secondary transformer winding of an LLC resonant converter is converted according to the invention to an arrangement in which the transformer with primary and secondary transformer winding additionally comprises the resonant inductor, as a result of which the magnetic resonant component parts of the LLC resonant converter are integrated in a component. What is accomplished in this way is that a resonant LLC resonant converter is provided, which is distinguished by efficiency and simplicity in the implementation while retaining the performance in the context of reducing complexity. Savings in the area of number of component parts, installation space, costs and weight and improved simplicity in terms of design can be achieved using the combined transformer according to the invention for the LLC resonant converter according to the invention.
Exemplary embodiments of the invention are explained in more detail below with reference to the drawings. For better clarity of illustration, the figures do not show a representation that is to scale or in proportion. In the figures, unless stated otherwise, identical reference signs denote identical parts with the same meaning.
In the drawings:
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.